This invention relates to a swash-plate type compressor for compressing refrigerant gas circulating in an air conditioning system, and more particularly to improvements in or to the lubricant oil feeding arrangement of the swash-plate type compressor.
In a swash-plate type compressor of this kind in general, rotation of the swash plate which is obliquely secured on the drive shaft causes reciprocating motions of the pistons within their respective cylinder bores to carry out pumping actions in cooperation with suction valves and discharge valves. The swash plate and the pistons engage each other with balls and shoes intervening therebetween in a manner that rotation of the swash plate is smoothly transduced into reciprocating motions of the pistons. According to this arrangement, the swash plate, the shoes, the balls and the pistons have their sliding contact portions subject to severe friction and therefore require to be permanently fed with lubricant oil.
Conventional lubricant oil feeding systems for feeding lubricant oil to the above sliding contact portions include a differential pressure type which is arranged such that the swash plate rotating in unison with the drive shaft splashes lubricant oil stored in the oil sump at the bottom of the cylinder block into oily mist which is fed to the above sliding contact portions and also guided to the low pressure chambers due to pressure difference between the swash plate chamber and the low pressure chambers which is caused by the reciprocating motions of the pistons within the cylinder bores, to lubricate radial bearings journalling the drive shaft, and their neighboring parts.
However, this differential pressure type has the disadvantage that there can occur a decrease in the amount of lubricant oil present within the compressor to lower the lubricant oil surface level in the oil sump so that the amount of lubricant oil splashed by the swash plate is temporarily reduced, resulting in insufficient lubrication of the aforementioned sliding contact portions and consequent seizure of these portions. Particularly, since the balls and shoes are subject to large sliding friction and fed with lubricant oil at a relatively small rate, they are more likely to seize than the other parts of the compressor such as the pistons, the cylinder bores and the radial bearings.
The reason for the aforementioned decrease in the amount of lubricant oil within the compressor is as follows: At the start of the compressor, rotation of the swash plate causes a sudden drop in the pressure within the oil sump to cause foaming of the lubricant oil so that a large amount of lubricant oil is delivered to the low pressure chambers due to the pressure difference between the swash plate and the low pressure chambers, and then sucked into the cylinder bores and discharged into the refrigerating circuit together with refrigerant gas. While circulating within the refrigerating circuit, the lubricant oil can stagnate at some places to be late in returning to the compressor. Further, refrigerant gas and lubricant oil can leak out of the refrigerating circuit, resulting in a reduced amount of refrigerant gas and lubricant oil which is returned to the compressor.